U.S. Pat. No. 3,943,579 discloses a container for a heat activated catalyst located between the intake of an exhaust blower and an incineration chamber. Fumes and gases generated during incineration are drawn through the catalyst which, if heated sufficiently, causes a chemical breakdown of the odor molecules, thereby preventing odor from entering the ventline. If, however, the catalyst has not reached its operative temperature, the odor is unaffected and creates an unacceptable nuisance.
Although the incinerator toilet disclosed in U.S. Pat. No. 3,943,579 has advantages, a few problem areas have developed. The catalyst container disclosed in the patent is located outside the incineration chamber, away from a direct source of heat, depending rather upon transferal of heat from the heated fumes as they pass through the catalyst. Unfortunately, the first gases passing through the catalyst also carry odor; hence, the odor passes through the cold catalyst into the ventline as odor and continues to do so until the catalyst reaches its operating temperature some several minutes later.
A secondary problem is that associated with condensation of moisture within the catalyst container unless higher temperatures, on the order of 200.degree. F., are reached. Condensation results in the accumulation of moisture underneath the canister.
To circumvent these problems the catalyst container was made an integral part of the incinerator, becoming a section of the double incinerator wall, having a portion of the wall perforated both front and back with a section of the annulus between the walls being filled with catalyst and heated directly by exposure to the inner heater of the incinerator chamber. Flow of gases and fumes through the catalyst was induced by the low pressure of the intake orifice of a downstream exhaust blower, collection of these gases immediately in the rear of the perforated section being accomplished by a manifold covering the perforated area. The catalyst chamber had a thickness of approximately 5/8"; a height of about 3 1/2"; and the arc of its inner wall was about 10" such that it had a total volume of 22 cu. in., approximately, for holding the heat activated catalyst. It also had a collection chamber with a depth of about 1/2" with an exhaust port with a diameter of about 1 1/2" located near the bottom of the outer wall of the collection chamber leading to the blower intake.
Efficiency of the catalyst is, among other things, a function of its volume, i.e., upon the dwell-time of the odor molecule. If the molecule is drawn through too rapidly, the time for the reaction is too short; therefore, if the thickness is small, then the areal extent must be large to provide the same volume or dwell-time within the catalyst. For the case immediately above, a large area of catalyst was provided as well as a correspondingly large collection chamber. However, the collection chamber was relieved at the other side by an orifice of only 1 1/2" within a distance of 1/2" from the outer face of the catalyst and this close proximity created an uneven distribution of pressure across face of the catalyst inducing more rapid flow immediately across from the exit orifice and lesser flow through areas farther removed from the orifice--effectively reducing the active or participating catalyst section. In short, the total area of the catalyst had to be enlarged by virtue of the small ratio of exhaust area to the total area of collection face due to the irregular distribution of pressure across the catalyst face.
Since the thickness of the catalyst bed was precisely that of the inside of the double incinerator wall, no provision could be made for the occasional replacement of replenishment of the catalyst. The catalyst used is activated alumina in the form of pellets approximately 1/8" diameter, very friable, hence subject to mechanical erosion, i.e., powdering, under the action of contraction and expansion of the inner incinerator wall due to heating and cooling. As the powder is generated, the effective volume of the catalyst shrinks, leaving a gap at the top of the catalyst allowing raw odor to pass through the blower and into the ventline.
A further consequence of the powder development is that of packing, i.e., powder closes off porosity of the catalyst, reducing flow-through and, hence, the effective volume or, with constant flow, reducing dwell-time of odor molecules within the catalyst. Even more damaging is the concentration of powder to the extent of becoming incompressible which causes the inner wall to deform when expanding, causing ultimate wall failure.
Finally, the powder is drawn into the blower, some of which adheres to the blower impeller causing imbalance and excessive vibration.